structures and union

8/3/2019 Structures and Union

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Structures and Union

To represent a collection of data

items of different types using asingle name.


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Why Structure

We have seen that arrays can be used torepresent a group of data items that belong tothe same type,such as int or float.

However we can not use an array if we want torepresent a collection of data items of differenttypes using a single name.

That can be done using structure.


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What is Structure

A structure in C is a heterogeneous userdefined data type.It groups variables into asingle entity.

A structure is a convenient tool for handlinga group of logically related data items.


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What is Structure

Arrays stores homgenous data wherestructuer can hold heterogeneous data.

Unlike arrays, structures must be definedfirst fo their format that may be used laterto declare structure variables.


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Structure Declaration

struct student{

char name[25];int age ;

float marks;};

Above declaration groups name,age and marks into a singleentity student.

struct is a reserved word.student is called structure tag or simply tag.This is the nameof the structure

NB: NO MEMORY IS ALLOCATED SO FAR.


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A new Type is defined by theProgrammer

student is a new type defined by the user,which canhold heterogenous data.

To use this structure student in a program we must create a

variable of type student as follows:

struct student x;Always remember to give the keyword struct before thestructure name while creating a variable.

x is a variable of type student.just like int z; z is a variable of type integer.


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Using structure variable

#include#includemain()

{

struct student{

char name[25];int age;float marks;

};

struct student x;


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Using structure variable

clrscr();printf("Enter name: ");scanf("%s",x.name);

printf("Enter age : ");scanf("%d",&x.age);printf("Enter marks:");scanf("%f",&x.marks);

printf(" \n\nName :%s \n Age :%d \nMarks:%.2f",x.name,x.age,x.marks);getch();

}


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Array of Structures

To maintain information about 10students,declare an array of studentstructure.

struct student x[10];

To store age of first student we writex[0].age=27;


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Pointers to structure

struct student x,*ptr;

ptr=&x;

ptr->age=27;


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A Program


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Unions

A union is a user defined data type in C whichallows the overlay of more than one variable inthe same memory area.

For example if a string of 200 bytes called filenameis required by first 50 lines of the code only andanother string called output of 400 bytes is

required by the rest of the code(i.e both stringsnot needed simultaneouly),it would be waste oftime to declare separate arrays of 200 and 400bytes


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structures and union

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